Radio link failure detection method and apparatus for wireless communication system

ABSTRACT

A radio link failure detection method of a user equipment transitioning between a Discontinuous Reception (DRX) mode and non-DRX mode cyclically in a wireless communication system includes transitioning between a Discontinuous Reception (DRX) mode and a non-DRX mode in a wireless communication system. The method also includes adjusting, when a mode transition occurs, a size of a monitoring window for a transitioned operation mode; reporting a radio channel condition acquired by monitoring and averaging the channel condition within the monitoring window; and repeating adjustment of the monitoring window size and report of the radio channel condition while moving the monitoring window as time progress.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/489,516,filed Apr. 17, 2017, which is a continuation of application Ser. No.12/590,312, filed on Nov. 5, 2009, now U.S. Pat. No. 9,629,029, whichclaims priority to Korean Application No. 10-2008-0109576, filed Nov. 5,2008, the contents of which are incorporated herein by reference intheir entireties.

BACKGROUND 1. Field

The present invention relates to wireless communications and, inparticular, to a radio link failure detection method of a user equipmenttransitioning between a Discontinuous Reception (DRX) mode and non-DRXmode cyclically in a wireless communication system.

2. Description of Related Art

Long Term Evolution (LTE), as the next evolutionary technology of the3rd generation mobile communication system known as Universal MobileTelecommunication Service (UMTS), is designed to provide improved highspeed packet data services based on the Orthogonal Frequency DivisionMultiplexing (OFDM).

FIG. 1 illustrates a diagram for an LTE system to which the radio linkfailure detection method of the present invention is adopted.

As shown in FIG. 1, an LTE system is characterized with the EvolvedRadio Access Network (hereinafter called E-RAN) 110 and 112 includingtwo infrastructure nodes: the Evolved Node B (hereinafter called ENB orNode B) 120, 122, 124, 126, and 128 and the anchor node 130 and 132. AUser Equipment (UE) 101 connects to the Internet Protocol (IP) networkvia an eNB and an anchor node. The eNB is connected to the eNB through aradio channel and responsible for cell and radio resource management.For instance, the eNB broadcasts the control information in the form ofsystem information within the cell, allocates radio resources to the UEsfor transmission and reception of data and control information, anddetermines handover of the UEs based on the channel managementinformation of the serving and neighbor cells. The eNB includes controlprotocols such as Radio Resource Control (RRC) protocol related to theradio resource management.

FIG. 2 illustrates a timing diagram for a Discontinuous Reception (DRX)mode operation of a UE in the LTE system of FIG. 1. The UE startsreception of Physical Downlink Control Channel (PDCCH) carrying theuplink/downlink scheduling information at the beginning of every DRXcycle and then communicates the data/control information throughDownlink Shared Channel (DSCH) and Uplink Shared Channel (USCH) based onthe scheduling information until a UE's DRX timer expires. The timerrestarts whenever the scheduling information destined to the UE istransmitted on the PDCCH. A DRX cycle length is divided into an activetime during which the UE receives the uplink/downlink schedulinginformation on the PDCCH and communicating the data/control informationthrough the DSCH and USCH until the time expires and an inactive timeduring which the UE switches off the uplink/downlink channels to saveenergy.

The durations of the active time and inactive time vary depending on theoperation of the DRX timer (in FIG. 2, the active time of the first DRXcycle is shorter than that of the second DRX cycle).

Meanwhile, the radio link between the UE and eNB can fail due to variouscauses, which is referred to as a Radio Link Failure (RFL). Additionallyan RLF detection mechanism is required to be defined in the LTE system.Typically, the RLF detection is performed such that the UE monitors theradio channel status to detect disconnection to the base station.However, no clear RLF detection mechanism for the UE operating in DRXmode as shown in FIG. 2 is specified in 3^(rd) Generation PartnershipProject (3GPP) standards. There is therefore a need of an RLF detectionmethod for the UE operating in DRX mode.

SUMMARY

To address the above-discussed deficiencies of the prior art, it is aprimary object to provide a RLF detection method for a UE transitioningbetween a DRX mode and a non-DRX mode in a wireless communication systemthat is capable of efficiently detecting the RLF and recovering from theRLF.

In accordance with an exemplary embodiment of the present invention, aradio link failure detection method for a user equipment transitioningbetween a Discontinuous Reception (DRX) mode and a non-DRX mode in awireless communication system includes adjusting, when a mode transitionoccurs, a size of a monitoring window for a transitioned operation mode;reporting a radio channel condition acquired by monitoring and averagingthe channel condition within the monitoring window; and repeatingadjustment of the monitoring window size and report of the radio channelcondition while moving the monitoring window as time progress.

In accordance with another exemplary embodiment of the presentinvention, a radio link failure detection apparatus transitioningbetween a Discontinuous Reception (DRX) mode and a non-DRX mode in awireless communication system includes a channel measurer that measuresthe radio channel to detect a radio link failure in a preset monitoringwindow; a transceiver that reports whether the radio link failure isdetected; and a controller that changes, when a mode transition occurs,a size of the monitoring window for the transitioned operation mode anddetects the radio link failure while moving the monitoring window astime progress.

In accordance with still another exemplary embodiment of the presentinvention, a radio link failure detection method for a user equipmenttransitioning between a Discontinuous Reception (DRX) mode and a non-DRXmode and including a first fixed monitoring window, a second fixedmonitoring window, and a variable monitoring window, in a wirelesscommunication system includes reporting, when a mode transition occursfrom the non-DRX mode to the DRX mode, a radio channel condition afteraveraging the channel conditions measured during the variable monitoringwindow; reporting the radio channel condition after averaging thechannel conditions measured during the second fixed monitoring windowwhen a predetermined time elapsed after the transition to the non-DRXmode; and reporting, when a time corresponding to the first fixemonitoring after the transition from the DRX mode to the non-DRX mode,the radio channel condition after averaging the channel conditionsmeasured during the first fixed monitoring window, the variablemonitoring window has a size between sizes of the first and second fixedmonitoring windows.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates a diagram for an LTE system to which the radio linkfailure detection method of the present invention is adopted;

FIG. 2 illustrates a timing diagram for a Discontinuous Reception (DRX)mode operation of a UE in the LTE system of FIG. 1;

FIGS. 3A-3B illustrate a timing diagram for an RLF detection methodafter the transition from the non-DRX mode to the DRX mode (in the firstperiod) according to an exemplary embodiment of the present invention;

FIG. 4 illustrates a timing diagram for an RLF detection method in a DRXcycle length (in the active time of the second period) according to anexemplary embodiment of the present invention:

FIG. 5 illustrates a timing diagram for an RLF detection method afterthe transition from the DRX mode to the non-DRX mode (the third period)according to an exemplary embodiment of the present invention;

FIG. 6 illustrates a flowchart for an RLF detection method according toan exemplary embodiment of the present invention. FIG. 6 is depictedwherein the UE transitions from the non-DRX mode to the DRX mode;

FIG. 7 illustrates a flowchart for an RLF detection method according toanother exemplary embodiment of the present invention; and

FIG. 8 illustrates a block diagram for a UE configured to support therlf detection method according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

FIGS. 3 through 7, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system. In the followingdescription, the terms “DRX operation mode” and “DRX mode” aresynonymously used, and the terms “non-DRX mode” and “continuous mode”are synonymously used.

In the following description, an RLF detection period is divided into afirst period of M DRX cycles starting at a transition from the non-DRXmode to the DRX mode, a second period equal to the duration operating inDRX mode, and a third period transitioning from the DRX mode to thenon-DRX mode.

Exemplary embodiments of the present invention are described withreference to the accompanying drawings in detail. The same referencenumbers are used throughout the drawings to refer to the same or likeparts. Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the present invention.

In an exemplary embodiment of the present invention, the RLF detectionmethod is proposed with the following operations of the UE in DRX mode.

1. M DRX cycles after transition from non-DRX mode to DRX mode (thefirst period):

In the first period, the UE monitors and averages the radio channelstatus according to the following options 1 and 2 and reports thesynchronization status, i.e., an in-sync or an out-of-sync, to thehigher layers according to the result value (here, the in-sync means aconnected condition of the radio and the out-of-sync means adisconnection condition between the UE and eNB).

Option 1: N1+n*DRX cycle length

Option 2: (n+k)*DRX cycle length

where, N1 denotes a duration for monitoring and averaging the radiochannel condition to detect the RLF in non-DRX mode (e.g., 200 ms (orfirst duration, identical hereinafter)), n denotes n^(th) DRX cycleafter transition from the non-DRX mode to the DRX mode, and k is 0 orpositive integer. Also, M cycles denote the elapse of time to the extentenough to determine the complete transition from the non-DRX mode to theDRX mode.

2. RLF detection method within a DRX cycle length (the second period)(applied after the transition from the no-DRX mode to the DRX moderegardless of before and after the M DRX cycles):

In the second period, the RLF detection method can be applied asfollowings depending on the difference between the active time lengthand N1 within the DRX cycle.

If N1 is greater than or equal to the active time in the DRX cycle(active time in the DRX cycle length ≤N1), the UE monitors and averagesthe radio channel condition during N2 and reports thein-sync/out-of-sync to the higher layers depending on the result value.

Otherwise, if the active time length in the DRX cycle is greater than orequal to N1 (active time in the DRX cycle length ≥N1), the UE monitorsand averages the radio channel condition during N1 and reports thein-sync/out-of-sync to the higher layers depending on the result value.

Where N1 denotes a duration for monitoring and averaging the radiochannel condition to detect the RLF in non-DRX mode (e.g., 200 ms (inthe present invention, setting the N1 value regardless of the abovedefinition is not ruled out)), and N2 denotes the duration formonitoring and averaging the radio link to detect the RLF in DRX mode.N2 before the M DRX cycles after the transition from the non-DRX mode tothe DRX mode can be defined as following:

N2=N1+n*DRX cycle length (option 1) (or the second time, identicalhereinafter) or (n+k)*DRX cycle length (option 2)

N2 after M DRX cycles following the transition from the non-DRX mode tothe DRX mode can be defined as following:

N2=M*DRX cycle length (or the third time, identical hereinafter)

3. After transition from the DRX mode to the non-DRX mode (the thirdperiod)

The UE monitors and averages the radio channel condition during the N2duration before the time N1 after the transition to the non-DRX mode,and reports the in-sync/out-of-sync to the higher layer depending on theresult value.

Also, the UE monitors and averages the radio channel condition duringthe N1 duration after the time N1 following the transition to thenon-DRX mode and reports the in-sync/out-of sync to the higher layerdepending on the result value.

Here N1 is a duration for monitoring and averaging the radio channelcondition to detect the RLF in the non-DRX mode (e.g., 200 ms (in thepresent invention, setting the N1 value regardless of the abovedefinition is not ruled out)), and N2 denotes the duration formonitoring and averaging the radio link to detect the RLF in DRX modeand can be defined as following in detail. First, the N2 before the MDRX cycle length after the transition from the non-DRX mode to the DRXmode can be defined as following:

N2=N1+n*DRX cycle length (option 1) or 9n+k)*DRX cycle length (option 2)

The N2 after the M DRX cycles following the transition from the non-DRXmode to the DRX mode can be defined as following:

N2=M*DRX cycle length

How the UE detects the RLF in the respective first to third periods hasbeen described schematically herein above. The RLF detection methodaccording to an exemplary embodiment is described in more detail withreference to accompanying drawings.

FIGS. 3A-3B illustrate a timing diagram for an RLF detection methodafter the transition from the non-DRX mode to the DRX mode, i.e., in thefirst period, according to an exemplary embodiment of the presentinvention.

In the duration of non-DRX mode, the UE monitors and averages the radiochannel condition for N1 and reports the in-sync/out-of-sync to thehigher layers depending on the averaging result value. As shown in FIGS.3A-3B, N1 acts as a moving window so as to progress along the(sub)frame. N1 can be defined as follow:

N1: duration for monitoring and averaging the radio channel condition todetect RLF in non-DRX mode (e.g., 200 ms)

The UE can regard the duration of the M DRX cycles after the transitionfrom the non-DRX mode to the DRX mode that the transition to the DRXmode in progress. In this case, the UE monitors and averages the radiochannel condition for the RLF detection duration according to thefollowing options 1 and 2 and reports the result value to the higherlayers.

Option 1: N1+n*DRX cycle length

Option 1: (n+k)*DRX cycle length

where N1 is the duration for monitoring and averaging the radio channelcondition to detect RLF in non-DRX mode (e.g., 200 ms), n is nth DRXcycle after the transition from the non-DRX mode to the DRX mode, and kis ‘0’ or positive integer.

In the meantime, the UE can regard the time when the M DRX cyclesfollowing the transition from the non-DRX mode to the DRX mode ends thatthe transmission to the DRX mode is complete. In this case, the UEmonitors and averages the radio channel condition for M*DRX cycle lengthand reports the in-sync/out-of-sync to the higher layers depending onthe result value (M=0 or positive integer).

As shown in FIGS. 3A-3B, the radio channel condition monitoring andaveraging duration defined in the active time of DRX cycle, i.e., theRLF detection period, progresses along the (sub)frame as a movingwindow. In FIGS. 3A-3B, the active time within the DRX cycle is shorterthan N1. When the active times within all the DRX cycles are longer thanN1, different operations are defined as described with reference to FIG.4.

According to the above described rules, the radio channel conditionmonitoring and averaging duration in each DRX cycle of the UE is asfollows:

In the example illustrated in FIGS. 3A-3B, M is set to 5 for M DRXcycles. That is, the UE completes the transition from the non-DRX modeto the DRX mode in 5 DRX cycles and regards the end of the 5 DRX cyclesas the start of the DRX mode.

First, the RLF detection period in the first DRX cycle 320 after thestart of the transmission to the DRX mode can be defined as N1+1*DRXcycle length or (1+k)*DRX cycle length 325.

Also, the RLF detection period in the second DRX cycle 330 after thestart of the transition to the DRX mode can be defined as N1+2*DRX cyclelength or (2+k)*DRX cycle length 335.

Also, the RLF detection period in the third DRX cycle 340 after thestart of the transition to the DRX mode can be defined as N1+3*DRX cyclelength or (3+k)*DRX cycle length 345.

Also, the RLF detection period in the fourth DRX cycle 350 after thestart of the transition to the DRX mode can be defined as N1+4*DRX cyclelength or (4+k)*DRX cycle length 355.

Finally, the RLF detection period in the fifth DRX cycle 360 after thestart of the transition to the DRX mode can be defined as N1+5*DRX cyclelength or (5+k)*DRX cycle length 365.

To help deeper understanding, the RLF detection period 325 in the firstDRX cycle duration 320 and the RLF detection period 335 in the secondDRX cycle duration 330 are compared. Here, the RLF detection period 335is longer than the previous RLF detection period 325 by as much as 1*DRXcycle length, and this is to obtain more samples as compared to theactive time in the non-DRX mode.

For the same reason, the RLF detection period 345 is longer than theprevious RLF detection period 335 as much as 1*DRX cycle length as muchas 1*DRX cycle length, and the RLF detection period 355 is longer thanthe previous RLF detection period 345 as much as I*DRX cycle length.

The measurement sampling times for the radio channel condition in theRLF detection period can be adjusted in consideration of fairnessbetween the no-DRX mode and the DRX mode, or the sampling times in thenon-DRX mode can be adjusted in consideration of the sampling times inthe DRX mode. That is, the sampling times in the non-DRX mode can bedefined as ‘a * sampling times in DRX mode’ (a is a decimal greater than‘0’ and positive integer).

FIG. 4 illustrates a timing diagram for an RLF detection method in a DRXcycle length, i.e., in the active time of the second period, accordingto an exemplary embodiment of the present invention.

In case that the active time of the DRX cycle length ≤N1, the UEmonitors and averages the radio channel condition for a duration N2 430and reports the in-sync/out-of-sync to the higher layers depending onthe result value. In case that the active time of the DRX cycle length≥N1, the UE monitors and averages the radio channel condition for theduration N1 420 and reports the in-sync/out-of-sync to the higher layersdepending on the result value. As shown in FIG. 4, the durations N1 andN2 are acting as moving windows so as to progress along the (sub)frame.Here, the duration N1 is a period (e.g., 200 ms (in an exemplaryembodiment of the present invention, setting the value of N1 regardlessof the above definition is not ruled out)) for monitoring and averagingthe radio channel condition to detect the RLF in non-DRX mode, and theduration N2 is a period for monitoring and averaging the radio channelcondition to detect the RLF in the DRX mode. The duration N2 can bedefined as follows. First, during the M DRX cycles following thetransition from the non-DRX mode to the DRX mode, the N2 is defined asfollowing:

N2=N1+n*DRX cycle length (option 1) or (n+k)*DRX cycle length (option 2)

Also, after the M DRX cycles following the transition from the non-DRXmode to the DRX mode, the N2 is defined as following:

N2=M*DRX cycle length

In FIG. 4, except for the last DRX cycle, the active time is shorterthan N1 420 in all the DRX cycles. In this case, the UE monitors andaverages the radio channel condition in the duration N2 430, for theactive times of these DRX cycles, and reports the in-sync/out-of-sync tothe higher layers depending on the result value.

Meanwhile, in cases of the active time 412 of the last DRX cycle 410,which is longer than N1 420, the UE monitors and averages the radiochannel condition in the duration N1 420 for the active time of the DRXcycle and reports the in-sync/out-of-sync to the higher layers dependingon the result value.

FIG. 5 illustrates a timing diagram for an RLF detection method afterthe transition from the DRX mode to the non-DRX mode, i.e., the thirdperiod, according to an exemplary embodiment of the present invention.

After the transition to the non-DRX mode 520, the UE monitors andaverages the radio channel condition in the duration N2 before the startof the duration N1 and reports the in-sync/out-of-sync to the higherlayers depending on the result value.

If the duration N1 is elapsed after the transition to the non-DRX mode530, the UE monitors and averages the radio channel condition in theduration N1 and reports the in-sync/out-of-sync to the higher layersdepending on the result value.

As shown in FIG. 5, the durations N2 and N1 act as moving windows so asto progress along the (sub)frame. Here, the duration N1 is a period(e.g., 200 ms (in an exemplary embodiment of the present invention,setting the value of N regardless of the above definition is not ruledout)) for monitoring and averaging to the radio channel condition todetect the RLF in non-DRX mode, and the duration N2 is a period formonitoring and averaging the radio channel condition to detect the RLFin DRX mode. The duration N2 can be defined as follows. First, duringthe M DRX cycles following the transition from the non-DRX mode to theDRX mode, the N2 is defined as following:

N2=N1+n*DRX cycle length (option 1) or (n+k)*DRX cycle length (option 2)

Also, after the M DRX cycles following the transition from the non-DRXmode to the DRX mode, the N2 is defined as following:

N2=M*DRX cycle length

FIG. 6 illustrates a flowchart for an RLF detection method according toan exemplary embodiment of the present invention. FIG. 6 is depictedunder the assumption of the situation where the UE transitions from thenon-DRX mode to the DRX mode.

Referring to FIG. 6, the UE is in the DRX mode with the start of the DRXcycle (block 601). With the start of the DRX cycle, the UE calculatesthe active time length within the DRX cycle (block 611) and compares theactive time and the duration N1 (e.g., 200 ms) to determines whether theactive time is greater than or equal to N1 (block 621). If the activetime is equal to or longer than N1, the UE monitors and averages theradio channel condition during N1 to detect RLF (block 631) and informsthe higher layers of the in-sync/out-of-sync depending on the resultvalue (block 641).

Otherwise, if the active time is not equal to or longer than N1, the UEdetermines whether the current DRX cycle is the M^(th) or later DRXcycle after the transition from the non-DRX mode to the DRX mode (block633). If the current DRX cycle is the M^(th) or later DRX cycle afterthe transition from the non-DRX mode to the DRX mode, the UE monitorsand averages the radio channel condition during the M^(th) or later DRXcycle (block 635) and informs the higher layers of thein-sync/out-of-sync depending on the result value (block 641).

Otherwise, if the current DRX cycle is not the M^(h) or later DRX cycle,the UE monitors and averages the radio channel condition during theduration ‘N1+n*DRX Cycle length’ (option 1) or ‘(n+k)*DRX cycle length(option 1) (block 637) and informs the higher layers of thein-sync/out-of-sync depending on the result value (block 641).

In FIG. 6, the operations following step 611 can repeat every (sub)frameduring the active time in the DRX cycle. At this time, the durations ofN1 and ‘N1+n*DRX cycle length/(n+k)*DRX cycle length, M*DRX cyclelength’ act as moving windows so as to progress along the (sub)frame.Detailed descriptions about the variables related to these durations aredescribed already with reference to the drawings, thereby being omittedherein.

FIG. 7 illustrates a flowchart for an RLF detection method according toanother exemplary embodiment of the present invention. FIG. 7 isdepicted under the assumption of the situation where the UE transitionsfrom the DRX mode to the non-DRX mode.

Referring to FIG. 7, the UE transitions from the DRX mode to the non-DRXmode (block 751). After the transition to the non-DRX mode, the UEcalculates the time elapsed after the transition to the non-DRX mode(block 761) and determines whether the calculated time is greater thanor equal to the duration N1 (e.g. 200 ms) (block 771). If the calculatedtime is greater than or equal to the duration N1, the UE monitors andaverages the radio channel condition during N1 for RLF detection (block773) and informs the higher layers of the in-sync/out-of-sync dependingon the result value (block 781).

Otherwise, if the calculated time is not equal to or greater than theduration N1, the UE monitors and averages the radio channel conditionduring N2 for RLF detection (block 775) and informs the higher layers ofthe in-sync/out-of-sync depending on the result value (block 781).

In FIG. 7, the operations following step 761 can repeat every (sub)frameafter the transition to the non-DRX mode. At this time, the duration N1and N2 act as moving windows so as to progress along the (sub)frame.Detailed descriptions about the variables related to these durations aredescribed already with reference to the drawings, thereby being omittedherein.

FIG. 8 illustrates a block diagram for a UE configured to support theRLF detection method according to an exemplary embodiment of the presentinvention.

As shown in FIG. 8, the UE includes a transceiver 801, a channelmeasurer 811, a DRX controller 821, an averaging window controller 831,a RLF detector 841, and a higher layer 851.

The transceiver 801 is configured to transmit and receive radio signals.

The channel measurer 811 is configured to measure radio channelcondition.

The DRX controller 821 controls the transition of the UE's operationmode between the non-DRX mode and the DRX mode and timers for managingthe DRX cycle length and active time within the DRX cycle.

The averaging window controller 831 controls the durations formonitoring and averaging the radio channel condition and determines thedurations for monitoring and averaging the radio channel condition usingthe information on the transition between the non-DRX mode and the DRXmode that is provided by the DRX controller 821 and the active timeinformation received by means of the transceiver 801. That is, theaveraging window controller 831 adjusts the length of the monitoringduration for RLF detection according to the transitioned operation modeand controls the movement of the detection window to detect the radiolink failure. The RLF detector 841 monitors and averages the radiochannel condition within the detection window determined by theaveraging window controller 831 and information the higher layer 851 ofthe in-sync/out-of-sync depending on the result value.

As described above, the radio link failure detection method of thepresent invention allows adjusting the radio link monitoring period inthe non-DRX mode and the DRX mode, thereby efficiently detecting theradio link failure.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for monitoring a radio link by aterminal in a wireless communication system, the method comprising:estimating a radio link condition based on channel conditions measuredduring a first evaluation period in a first reception mode; for aduration of time after transitioning from the first reception mode to asecond reception mode, estimating a radio link condition based onchannel conditions measured during an evaluation period, the evaluationperiod used during the duration of time in the second reception mode;and estimating a radio link condition based on channel conditionsmeasured during a second evaluation period in the second reception mode,after the duration of time, wherein the evaluation period is not lessthan a minimum of the first evaluation period and the second evaluationperiod.
 2. The method of claim 1, wherein the first reception mode isone of a Discontinuous Reception (DRX) mode and a non-DRX mode and thereception second mode is another of the DRX mode and the non-DRX mode.3. The method of claim 1, wherein the duration of time is equal to thesecond evaluation period.
 4. The method of claim 1, wherein theevaluation period is not less than the first evaluation period based onthe first evaluation period being shorter than the second evaluationperiod.
 5. The method of claim 1, wherein the evaluation period is notless than the second evaluation period based on the second evaluationperiod being shorter than the first evaluation period.
 6. The method ofclaim 1, wherein, if the first reception mode is a non-DRX mode, alength of the first evaluation period is a preset value.
 7. The methodof claim 1, wherein a length of the first evaluation period is 200milliseconds (ms).
 8. The method of claim 1, wherein a length of thefirst evaluation period or the second evaluation period is defined as Mcycles times a DRX cycle length, wherein M is an integer.
 9. The methodof claim 8, wherein the M cycles denote an elapse of time sufficient todetermine a complete transition from the first reception mode to thesecond reception mode.
 10. The method of claim 1, wherein the evaluationperiod is an arbitrary value plus a minimum among the first evaluationperiod and the second evaluation period.
 11. A terminal for monitoring aradio link in a wireless communication system, the terminal comprising:a transceiver configured to transmit and receive a signal; and at leastone processor configured: to estimate a radio link condition based onchannel conditions measured during a first evaluation period in a firstreception mode, for a duration of time after transitioning from thefirst reception mode to a second reception mode, to estimate a radiolink condition based on channel conditions measured during an evaluationperiod, the evaluation period used during the duration of time in thesecond reception mode, and to estimate a radio link condition based onchannel conditions measured during a second evaluation period in thesecond reception mode, after the duration of time, wherein theevaluation period is not less than a minimum of the first evaluationperiod and the second evaluation period
 12. The terminal of claim 11,wherein the first reception mode is one of a Discontinuous Reception(DRX) mode and a non-DRX mode and the second reception mode is anotherof the DRX mode and the non-DRX mode.
 13. The terminal of claim 11,wherein the duration of time is equal to the second evaluation period.14. The terminal of claim 11, wherein the evaluation period is not lessthan the first evaluation period based on the first evaluation periodbeing shorter than the second evaluation period.
 15. The terminal ofclaim 11, wherein the evaluation period is not less than the secondevaluation period based on the second evaluation period being shorterthan the first evaluation period.
 16. The terminal of claim 11, wherein,if the first reception mode is a non-DRX mode, a length of the firstevaluation period is a preset value.
 17. The terminal of claim 11,wherein a length of the first evaluation period is 200 milliseconds(ms).
 18. The terminal of claim 11, wherein a length of the firstevaluation period or the second evaluation period is defined as M cyclestimes a DRX cycle length, wherein M is an integer.
 19. The terminal ofclaim 18, wherein the M cycles denote an elapse of time sufficient todetermine a complete transition from the first reception mode to thesecond reception mode.
 20. The terminal of claim 11, wherein theevaluation period is an arbitrary value plus a minimum among the firstevaluation period and the second evaluation period.